1. Field of the Invention
This invention relates to a video recording and reproducing apparatus in which image signals are divided into plural channels and recorded and reproduced.
2. Description of the Prior Art
A high-definition television system (Hi-Vision) has been proposed recently, which can display a wider image at higher resolution in comparison with existing television systems. The high-definition television system has 5 or more times the data volume as compared with the conventional television system. So when the data is recorded in a conventional video disc, the available recording time is much shorter. On the other hand, the MUSE, (Multiple Sub-Nyquist Sampling Encoding) system developed by NHK, (Nihon Hoso Kyokai, or the Japanese Broadcasting Corporation), can broadcast the high-definition television signals through one of the satellite broadcasting channels by band-compressing the signals (Ninomiya, et al.: Development of the MUSE System, NHK Technical Study Report Vol. 39-2). By using the MUSE signals in which the high-definition television signals are band-compressed, longer recording times of the video disc can be obtained. When the high-definition television data is band-compressed, it becomes an analog signal having an of 8.1 MHz signal bandwidth. The bandwidth of MUSE signals is approximately two times that of the existing television signals. Therefore, when the same shortest recording wavelength as in a video disc in which existing television signals are recorded, the linear velocity required in recording and reproducing approximately doubles. To cope with this, the innermost circumferential radius should be enlarged, or the rotating speed of disc should be higher. If the innermost circumferential radius is enlarged, the available recording time of the disc becomes shorter. If the rotating speed of the disc is increased, the motor which rotates the disc must bear a heavier load. A laser beam in an optical video disc is controlled to focus along the track of the disc during recording and producing. When the rotating speed becomes higher, the bandwidth of the controlling system must be wider, and the control tends to be unstable.
In addition, by dividing, the MUSE signal into plural channels and recording them in parallel, the linear velocity can be reduced. In the channel-division recording system, division points and composition points of video signals must be matched. Therefore, the video signals must be synchronized during recording and reproducing. In recording, the synchronization is possible by using the input MUSE signals, but in reproducing, the reproduction signals must be used for the synchronization. Synchronous signals are conventionally newly added for the synchronization in image reproduction. For this purpose, a part of the video signals are replaced with synchronous signals, or the time axis of the video signals is compressed to insert synchronous signals. In the case of substituting with synchronous signals, some of the video signals are lost. When the video signals are time-compressed, on the other hand, to insert synchronous signals, the signal bandwidth must be wider.
In the channel-division recording system, since the video signals are time-expanded or time-compressed, it is necessary to convert the video signals into digital signals once and store them in a memory. As the MUSE signals transmit sample values in an analog system, however, it is necessary to strictly match sampling phases in the case of sampling at the same frequency. A synchronous signal that can detect a phase error is required to, match the sampling phases, and the processing circuit becomes complicated. In addition, although the sampling phases do not have to be matched when the sampling is performed at higher frequency than the sampling frequency of the MUSE signals, a larger volume of data must be stored in a memory.